Filters of this kind have already been disclosed. Their manufacture involves folding a continuous length of paper, in conjunction with which the size of the pleats and their positions in relation to one another are determined by precise and uniform folding of the paper and by feeding the paper for securing by means of gluing or the bonding-on of an edge strip. The form imparted to the pleats is determined by the conditions associated with the manufacture of the pleats and the feeding of the continuous length of folded material, and variations in these conditions and in the characteristics of the paper will result in uneven pleats, which are then secured in the state which has been imparted to them.